This invention relates to an optical disk device, and in particular, relates to a method of identifying the type of an optical disc loaded therein.
Optical disc is generally classified into CD (Compact Disc), DVD (Digital Versatile Disc), and BD (Blu-ray Disc). Furthermore, there are a plurality of types, such as ROM (read only), -R (writable), and -RE (rewritable), in each kind of disc; playing conditions are different depending on the type of disc. For this reason, an optical disk device is required to identify the type of a disc loaded therein.
Conventionally, optical disc devices identify the type of disc through any one of the following methods to perform playing sequences differing depending on the type of disc:
(1) a method of reading management information recorded in a Burst Cutting Area (BCA) to identify the type of disc by the read management information;
(2) a method of identifying the type of disc by Differential Phase Detection (DPD) amplitude; and
(3) a method of identifying the type of disc by RF amplitude.
For example, JP2007-18581A discloses a technique related to this invention.
As described above, there are various methods for an optical disc device to identify the type of a disc loaded therein. The above-described method (1) enables reliable disc identification because the disc standard stipulates that the type of disc must be recorded in management information (a BCA). Actually, however, there are discs without BCAs. Furthermore, if a BCA is unclean or scratched, the BCA data might be unable to be read from the disc.
DPD is used for tracking adjustment, but tracking adjustment can be made through other methods. Therefore, in an optical disc device which does not employ the DPD, the method (2) cannot be used.
The method using RF signal amplitude utilizes the phenomenon that the intensity of a signal obtained from the return light from a data area, in which data is written, differs depending on the disc, namely, that ROM type discs have greater reflectance and RF amplitude is likely to be larger because of their structure, while -R and -RE type discs have smaller reflectance. However, the reflectance of disc considerably varies among discs, so the identification using reflectance has been less reliable.
For these reasons, the type of a loaded disc sometimes cannot be identified exactly even through the above-described three methods. A method for exactly identifying the type of disc has been desired.
An object of this invention is to provide a method of identifying the type of a loaded disc, particularly whether the disc is a read only (ROM) disc or a writable (-R or -RE) disc.